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MG MG Y Type - YA Headlights


Can some kind soul please clarify a few points regarding the headlight wiring on the YA?
I only get headlight illumination on one dipper switch position. As the wiring diagram indicates that lead 7 is only connected on export models perhaps this is what should happen. My confusion is that my car has both wires at the headlamp end, and as purchased the headlamps both have 35W/35W bulbs fitted. Unfortunately, I didn't check the lights before purchase so I don't know if the lights have ever worked on both settings. So far I have not managed to get to the back of the dipper switch so I have yet to establish whether lead 7 is connected to the dipper switch. The questions therefore are as follows:
• Is illumination on only one switch setting normal or is there a fault in the dipper switch? Neil Cairns article “An Introduction to the MG Y Series“says that the car has no main beam light but presumably that comment refers to a main-beam 'warning' light.
• If it is normal (for non-export cars) did drivers really pass oncoming vehicles on sidelights only?
• In the event that there is a fault in the dipper switch how is the switch removed? I can see the securing screws on the toe plate but are they using captive nuts on the engine side? Can the switch be removed into the car or must it be removed from underneath?
• If wired as for export (lead 7 connected) and dipper working correctly what is the difference in headlight beam between the two dip switch positions (35W/35W bulb fitted)?
• Finally, I am considering fitting modern halogen replacement headlight bulbs. Is 35W/35W the correct wattage to fit? My car is still positive earth and has a standard dynamo fitted.
As always, I am grateful for any expert input
Don (Y4293)
D G Avery

Don

Irrespective of how the dip switch is set current should be going through at least one filament of each bulb. The thing to check first is that both filaments on both bulbs are OK. No there is no Main Beam Warning light on the dash for the driver.

At the switch there should be:
1) 2 Red with Black leads (#7) connected to one terminal,
2) 2 Yellow with blue leads (#9)connected to the other lower terminal.
3) As you look at the switch on the firewall standing in front of the car the #7 leads are on the left, and the #9 leads are on the right.
4) The Blue (#14) lead is connected to the higher screw connector.

That covers the correct layout of the switch.

Next you need to check that you have a circuit between each #7 or #9 and the bayonet connector at the lamp, so if you do not have clip on leads on your ohmmeter you will need to engage an assistant to hold the lead onto one terminal and then the other while you connect to the lamp fitting inside the headlamp, and then the other. Your assistant should leave their lead connected to one fitting while you check both lamp connectors as if you get a full circuit irrespective of which lead they are connected to on both leads at the lamp end you have a melted wire somewhere in the loom where the two have fused together. This will give you the effect of current going to each bulb irrespective.

The "pass lamp" as it was called refers to the single Lucas FT57 or SFT575 fog lamp.

Removal of the switch is indeed by undoing the two toe board screw. The switch then drops off into the engine bay. Normally there are not captve nuts on the back. Normally the screws tap directly into the switch plate itself which can make for fun when you come to reassemble as you align the screws up with the right hole on the switch plate - I have just fitted on of these to a Y/T I am building up. It is much easier when the engine is out of the car (which is how I am dealing with it) as you can stand in the engine bay and reach through the gearbox opening to position the switch while you put the toe board screws in.

Not sure what you mean by "wired for export" as irrespective of market, both lamps had both #7 and #9 leads connected to both lamps and each respective side of the switch. You should have 5 wires at the switch in two sets of 2 and one on its own.

Fitting the correct halogen bulb should not make any difference to the way the leads are connected. I fitted halogen bulbs to my Y many years ago and they just twisted into the existing loom fittings.

Hope that helps you Don,

Paul

Paul Barrow

Paul,

Thank you for your input - as always, very informative.

Perhaps I was being misled by the comment on the wiring diagram which says “Lead No7 from Dipper Switch to Dip Filament (shown dotted) only connected on export models”. Having not yet managed to access the back of the switch I wondered if my Lead No 7 could be disconnected at the back of the switch; this would have given the symptoms that I am experiencing. From your explanation this will/should not be the case.

I had already done the check you suggested for a supply starting at lead No 14 source at the junction box to both the terminals on the bulb holder at each headlight. I ‘initially’ noted a supply to only one lead (No 9) at each light. However, on repeating the test since my first post I have now noticed that I do indeed get a supply to the other lead – but only for the time that the switch is depressed. As soon as foot pressure is released the supply disappears. Fairly conclusive evidence (I think) that the switch is kaput. I am not looking forward to replacing it after reading your words!! My engine bay is full of engine and gearbox!

However, I still don’t understand how the beam changes just by switching filaments particularly as both filaments are of the same wattage and I see no deflector within the bulb.

Re your remark about the passing light, this would tend to support the idea that at one time operating the dip switch would actually turn off the headlights. Hence the note on the wiring diagram. As the passing/fog light is not in the headlight circuit I assume it would have to be switched on at all times so as to be available when the headlights were dipped.

I think the halogen route is also the way I want to go. The current old style 35W/35W bulbs are very yellow and produce a very poor light for modern motoring conditions. In the absence of any comment from you to the contrary, I assume that 35W is correct. In any case, I doubt the dynamo would cope with much more!!

Clearly, (pun intended) halogen is the way to go.
Thanks again for your input.
Don
D G Avery

Hi Don

Dont worry - you said "My engine bay is full of engine and gearbox!" - its just a lot easier without all that. All you need is a willing volunteer helper to either hold it in position (preferbly) on a crawl board under the car if you dont have a pit or lift, while the other secures it in with the toe board screws.

Dip switch only ever controlled the headlamps - the fog lamp was only ever a seperate switch on the dash side - sorry if I wasnt clear there. Why the heck it ever got called a pass lamp beats me ... but I am sure there is a logical explanation!

I will look up my contacts and add a supplier for halogen bulbs for the Lucas S700 headlamsp with a bayonet fitting that will make that part of it so much easier for the conversion. The bulbs arent cheap ... but then safety isnt either.

Never having taken one of these switches apart I do not know if they are user servicable - but I wouldnt have thought that they were that hard. If you want to take it out and send it to me I will have a play and get it firing for you if you like if I can.

The important thing is do you have continuity on #7 at the switch to one terminal in each light only, and continuity from #9 at the switch to one terminal in each light only. I think, from my reading of the circuit the dip filament goes out when the main beam is lit so you should not have continuity on both lamp terminals from one switch terminal. As before, if you have this, then you have a melted wire in the harness, or another loose wire touching somewhere.

Paul



Paul

Paul Barrow

I fitted halgoen bulbs 10 years ago. Got them from Anthony Pearson in Australia. He recomended 35/35 as the 50 watt is too much drain.They work well and are twice as bright as the old incadesnt bulbs. Terry
Terry O'Brien

This thread was discussed between 21/07/2011 and 22/07/2011

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